1. Technical Field
The present disclosure relates generally to coatings for filaments. More particularly, the present disclosure relates to silicone coatings for filaments or sutures formed by a plasma polymerization process.
2. Background of Related Art
Many synthetic materials are presently used as surgical sutures. These materials may be used as single filament strands, i.e., monofilament sutures, or as multifilament strands in a braided, twisted or other multifilament construction. Synthetic sutures have been made from materials such as polypropylene, nylon, polyamide, polyethylene, polyesters such as polyethylene terephthalate, and segmented polyether-ester block copolymers. In addition, absorbable synthetic sutures have been prepared from synthetic polymers such as polymers containing glycolide, lactide, dioxanone, caprolactone, and/or trimethylene carbonate. Natural materials have also been used to make sutures. For example, silk has been used to make non-absorbable sutures. As another example, catgut sutures are absorbable sutures made from a natural material.
Sutures intended for the repair of body tissues must meet certain requirements: they must be non-toxic, capable of being readily sterilized, they must have good tensile strength and have acceptable knot-tying and knot characteristics. The sutures should also be sufficiently durable from the point of view of fray resistance.
The performance of a suture in terms of knot run down, knot security and tissue drag are particularly important to surgeons. Knot run down performance, which reflects the ease of placement of a knot tied in a suture, is important in surgical procedures where it is necessary that a knot be tied in a suture when the knot is deep inside a surgical or natural opening. For instance, a dental surgeon may need to tie a knot inside a patient's mouth. An intravaginal hysterectomy requires suturing in restricted quarters. One technique frequently used is to tie a square knot that can be run down from an exterior location where the knot is first tied to lie against tissue with a desired degree of tightness. The knot is snugged down so that it is holding with a degree of firmness chosen by the surgeon for a particular situation and then additional throws, utilized to form additional knots, are tied down against the first throws of the square knot. In some instances, the first throw is a double twist followed by a single throw to form a surgeons' knot, with additional throws to form additional square knots on top as needed. The ease with which a knot runs down the suture depends on a number of factors such as composition of the suture, braid structure of the suture, and the nature of the coating, if any, applied to the suture. Preferably, the knot runs down the suture smoothly and easily.
Knot security is the ability of the knot to hold without slipping for an acceptable length of time. The characteristics of the suture material which allow a knot to hold securely are somewhat at odds with the characteristics of the suture material which provide satisfactory knot run down performance, since knot security requires that the suture grab itself while knot run down requires that the suture pass smoothly over itself. Accordingly, a balance of these two characteristics is normally required.
Some synthetic sutures, especially polypropylene monofilament sutures, have a tendency to fray as the suture passes over itself, e.g., when tying knots. While the limited amount of fraying exhibited by these sutures does not substantially hamper the performance of the suture, there remains room for improvement in the processing and the characteristics of such sutures.
It is also desirable for a suture to have low tissue drag, which is a measure of the force required to pull a suture through tissue. High drag forces result in chatter as the suture passes through tissue, make it more difficult for the surgeon to align tissue neatly, and increase the time to complete the closure being made with the suture.
A wide variety of coatings have been applied to sutures of various types to improve one or more characteristics of the suture. See, for example, U.S. Pat. Nos. 3,187,752; 3,527,650; 3,942,523; 4,105,304; and 4,185,637. These coatings include silicones. See U.S. Pat. No. 3,187,752.
Fibers or textile treatments which include organo silicon compounds have been described in, inter alia, U.S. Pat. Nos. 3,280,160; 3,418,354; 4,283,519; 4,359,545; 4,217,228; 4,784,665; 3,837,891; 4,207,071; 4,184,004; 4,578,116; 4,937,277; 4,617,340; and 4,624,676.
Siloxane-oxyalkylene copolymers have been described in U.S. Pat. Nos. 3,629,310; 3,755,399; 3,280,160; 3,541,127; and 4,699,967. U.S. Pat. No. 5,383,903 discloses coating a surgical suture with a dimethylsiloxane-alkylene oxide copolymer lubricant.
The above coatings are applied by means known to those skilled in the art, e.g., dipping, spraying, etc.
It would be advantageous to apply coatings possessing improved mechanical strength to sutures in order to further enhance the sutures' handling characteristics.